1. Field of the Invention
The present invention relates to an auto-toner sensor for controlling the toner density in a process of developing a latent image obtained from a manuscript.
2. Description of Prior Art
In general, an auto-toner sensor using a sensor such as a magnetic type sensor is provided in the copy machine utilizing a two-component developing method by electrophotography in order to maintain the density of the toner at an appropriate level.
Such an auto-toner sensor is shown in FIG. 1. In this auto-toner sensor, a control voltage V.sub.cnt obtained as a power supply voltage V.sub.cc divided by a variable resistance VR is applied to a control terminal of a sensor 10, which affects the sensitivity in toner density detection. In response to this control signal V.sub.cnt, the sensor 10 detects a toner density and produces a sensor output voltage V.sub.out which is a DC voltage proportional to the detected toner density.
In such a conventional auto-toner sensor, it is necessary to adjust the variable resistance initially such that the sensor output voltage V.sub.out for toner of standard density is equal to a predetermined standard value. The toner is absorbed on the latent image obtained from the manuscript at an appropriate level only after the sensor output voltage V.sub.out is adjusted with respect to the standard value by this initial adjustment.
Now, the sensor output voltage V.sub.out may vary because of the variation in the sensitivity of the detection by the sensor 10, an environmental condition of the copy machine such as a humidity, and the variation of the toner density. As a result, in the conventional auto-toner sensor, the initial adjustment of the sensor output voltage V.sub.out with respect to the standard value has to be carried out by the operator manually.
However, due to the subtlety of the toner absorption by the drum, high accuracy is required for this adjustment, and this has proven to be enormously cumbersome operation for the operator to perform.